The invention relates to a method for operating an internal combustion engine. The invention also relates to a device for the control and/or regulation of an internal combustion engine having a motor regulator and an injection processor module which are designed for carrying out the method. The invention also relates to an injection system having a motor, which has a common rail for an internal combustion engine with a number of cylinders, and having a number of injectors assigned to the cylinders, wherein an injector is assigned an individual accumulator which is designed for holding fuel from the common rail available for injection into the cylinder. The invention also relates to an internal combustion engine having a motor, which has a number of cylinders, and having an injection system with a common rail and with a number of injectors, wherein an injector is assigned an individual accumulator which is designed for holding fuel from the common rail available for injection into the cylinder.
In an internal combustion engine, the start of injection and the end of injection are significant in determining the quality of the combustion and the composition of the exhaust gas. To comply with legal limit values, these two characteristic variables are commonly regulated by an electronic control unit, which may be a separate module for injection control and/or regulation or may be a part of an engine regulator (ECU). In this way, it is possible, depending on demand, to specify an injection quantity parameter, such as for example the injection quantity of the fuel itself or some other suitable injection quantity parameter which is significant for the injection quantity, that is to say from which the injection quantity of the fuel can be inferred, in particular from which the injection quantity of the fuel can be calculated, reliably assumed, estimated or reliably determined in some other way. If appropriate, it is possible for the injection quantity parameter itself rather than the injection quantity of the fuel to be taken into consideration for further measures. An appropriate injection quantity parameter of said type may in particular be an injection duration of the injector and/or an energization duration of an injector. As significant parameters for this purpose, use may be made of the start of injection, an end of injection, or a start of energization for an injector, an end of energization for an injector, or any desired combination of these and other injection quantity parameters. On the basis of such determinations, which are directed in particular to the injection duration or similar injection quantity parameter or the injection quantity itself, it is possible as a result to make a statement regarding the fuel quantity actually used for working cycle of a cylinder. This is compatible with engine running and the compliance with emissions regulations and is important not only in steady-state running but increasingly also for transient running during engine operation.
The concept of an injector with an individual accumulator has been proven in the context of a common-rail injection system as described for example in DE 199 35 519 C2. The individual accumulator is supplied with pressurized fuel from the pressure port via a fuel inflow duct and is directly connected in terms of flow to the high-pressure duct for the highly pressurized fuel in the common rail. The volume of the individual accumulator is large compared with the volume of the high-pressure duct and of the nozzle prechamber in the injector. Owing to the arrangement of the injector—if appropriate decoupled from the common rail by way of a throttle element—there is adequate space available in the individual accumulator in the housing of the fuel injector for holding fuel available for at least one entire injection quantity for a working cycle of a cylinder, or at any rate for a partial injection during the course of the working cycle.
A method for the regulation of an internal combustion engine having a common-rail system together with individual accumulators is known from DE 10 2007 037 037 B3, in which an injection duration for the actuation of the injectors is calculated; this is performed on the basis of rotational speed regulation of an outer regulation loop and injection duration regulation of an inner regulation loop.
DE 103 44 181 A1 describes an internal combustion engine having a common-rail system including individual accumulators, approximately as is schematically shown in FIG. 1. The fuel pressure of the individual accumulators is detected during a measurement interval and stored. On the basis of the stored pressure values, an end of injection is determined, and a virtual start of injection is calculated.
DE 10 2009 002 793 A1 describes a method in which, for a multiple injection, the pressure of a high-pressure source and the pressure of an individual accumulator are used.
To better satisfy the requirements mentioned in the introduction, a multiple injection has proven to be particularly advantageous. It is common in the case of multiple injections—that is to say in particular with a main injection (HE) and a pre-injection (VE) and/or a post-injection (NE)—to assume that system pressure prevails for an injection, and in particular to assume that system pressure prevails also for a subsequent injection, that is to say that the system at the injector is acted on with a pressure of the common rail. While this is basically correct, it has nevertheless likewise proven relevant, for multiple injections in the case of a common-rail system including individual accumulator and injector of the type discussed in the introduction, for the pressure of the common rail to be assumed to be the system pressure actually relevant for the injection quantity throughout; that is to say both for a main injection and for a secondary injection. In the case of an injection system in the form of a common-rail system with individual accumulator and injector, it is desirable to control a fuel quantity during a multiple injection in an improved manner, in particular to determine an injection quantity for a subsequent injection in a particularly reliable manner and/or in an improved manner.